In facilities for plating by passing a material to be plated through a bath of molten metal such as zinc or aluminum, a conductive liquid, the molten metal is held by a method as described in Japanese Laid-Open Patent Publication No. 356/92. In this method an opening portion is provided at the bottom of an aerial pot from a material poorly wettable by molten metal, and utilizes the surface tension of the molten metal to hold the molten metal inside the aerial pot. This method is limited in increasing the height of the molten metal that can be held.
To achieve an increased height of molten metal which can be held in a container Japanese Laid-Open Patent Publication No. 109148/88 discloses a technique of providing a pressure chamber for accommodating a gas under the container storing molten metal. This technique involves a pressure chamber containing gas connected to an opening at the bottom of the molten metal container, and raising the gas pressure inside the pressure chamber, thereby increasing the height of the molten metal held in the molten metal container. The technology disclosed in this publication, however, has the disadvantage that even when the pressure (gravitational) of the molten metal at the opening balances statically with the gas pressure inside the pressure chamber, the difference in density between the gas and the molten metal causes the gas to penetrate the molten metal as bubbles and go up through the molten metal.
To obtain a plating of satisfactory quality by passing a material to be plated through molten metal, it is desired that the height of the molten metal be kept high and constant, and avoid gas bubbles in the molten metal.
An object of the present invention is to enable molten metal to be held at a predetermined height in a container with an opened bottom.
Another object of the invention is to prevent the formation of gas bubbles in molten metal.
Still another object of the invention is to produce a plating of satisfactory quality by hot dipping.